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Wednesday, January 20, 2010

The Sloan Digital Sky Survey is the largest survey of our observable universe. This video demonstrates just how much they have mapped.

I don't know why things like Sloan don't get as much hype as other experiments. The knowledge we get from Sloan is priceless. Sloan, more than anything else, lets us see what the large scale structure of the universe is.

However, here's to the hope that the upcoming 21 cm experiments will make Sloan look like a small time survey! You see that space between the observed galaxies from Sloan and the CMB? 21 cm experiments may be able to map most of it. Pretty impressive.

In answer to the question, "How much of the observable universe have we mapped?" I would say that the answer appears to be, "Next to nothing." It looks like we have a long way to go before we can say that we even have a complete map of the nearby universe.

It is interesting that I stumbled upon these comments, because Miguel is my advisor. So CARPE is a speculative instrument design for a cosmology radio telescope (also of course there is the SKA, but it turns out that many of the design decisions being made for the SKA may not be optimal for...). CARPE has three primary science goals which are 21 cm intensity mapping, surveying pulsars, and pulsar timing.

The nature of radio observing is such that the distribution of antennae is critical. For CARPE's science it is optimal to have many antennae receiving elements all very tightly packed to get the best field of view on the sky, however tightly packing the antennae results in poor angular resolution. In the case of 21cm mapping, that large scale structure is so, well large, this loss of resolution is not a problem, but actually a benefit with respect to signal to noise.

For pulsars you need to have a wide field of view to find them. Then in order to detect gravitational waves you treat each pulsar that you can detect as a clock. Just like a general relativity cartoon diagram where each point in space time has a clock sitting at that location. A passing gravitational wave will delay the pulsars regular beat, however it remains to be seen if this technique is possible with observational noise (pulsar glitches, ionospheric corrections, etc.).

I agree that 21 cm experiments have the potential to map large portion of the universe and will be an important tool in cosmology. See the MWA for example.